Adjust the order of linux kernel header include paths

The current order of include paths could cause the following error:

In file included from /virtual/main.c:3:
In file included from include/linux/sched.h:13:
In file included from include/linux/pid.h:4:
In file included from include/linux/rculist.h:10:
In file included from include/linux/rcupdate.h:38:
In file included from include/linux/spinlock.h:50:
In file included from include/linux/preempt.h:80:
In file included from /lib/modules/4.12.14-197.45-default/build/arch/s390/include/generated/asm/preempt.h:1:
include/asm-generic/preempt.h:10:42: error: no member named 'preempt_count' in 'struct thread_info'
        return READ_ONCE(current_thread_info()->preempt_count);
               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
include/linux/compiler.h:349:34: note: expanded from macro 'READ_ONCE'
                     ~~~~~~~~~~~~^~~~~
include/linux/compiler.h:342:17: note: expanded from macro '__READ_ONCE'
        union { typeof(x) __val; char __c[1]; } __u;
\
...
7 errors generated.

It's supposed to load "asm/preempt.h" from "source/"(*) but accidentally
loaded the one from "build/", so the error showed.
(x86_64 didn't suffer this error because it didn't install the extra
 "asm/preempt.h" to "build/".)

For the distros, e.g. SUSE/openSUSE and debian,  with separate "build/"
and "source/", all those "generated/" paths only exist in "build/". To
avoid the potential compilation issue, this commit adjusts the include
order for those with split headers to align the include order from
kernel top Makefile.

(*) /lib/modules/4.12.14-197.45-default/source/arch/s390/include/

Signed-off-by: Gary Lin <[email protected]>

src/cc/frontends/clang/kbuild_helper.cc

@@ -74,27 +74,47 @@ int KBuildHelper::get_flags(const char *uname_machine, vector<string> *cflags) {
  cflags->push_back("-isystem");
  cflags->push_back("/virtual/lib/clang/include");
 
- // some module build directories split headers between source/ and build/
+ // The include order from kernel top Makefile:
+ //
+ // # Use USERINCLUDE when you must reference the UAPI directories only.
+ // USERINCLUDE := \
+ // -I$(srctree)/arch/$(SRCARCH)/include/uapi \
+ // -I$(objtree)/arch/$(SRCARCH)/include/generated/uapi \
+ // -I$(srctree)/include/uapi \
+ // -I$(objtree)/include/generated/uapi \
+ // -include $(srctree)/include/linux/kconfig.h
+ //
+ // # Use LINUXINCLUDE when you must reference the include/ directory.
+ // # Needed to be compatible with the O= option
+ // LINUXINCLUDE := \
+ // -I$(srctree)/arch/$(SRCARCH)/include \
+ // -I$(objtree)/arch/$(SRCARCH)/include/generated \
+ // $(if $(building_out_of_srctree),-I$(srctree)/include) \
+ // -I$(objtree)/include \
+ // $(USERINCLUDE)
+ //
+ // Some distros such as openSUSE/SUSE and Debian splits the headers between
+ // source/ and build/. In this case, just $(srctree) is source/ and
+ // $(objtree) is build/.
  if (has_source_dir_) {
- cflags->push_back("-I" + kdir_ + "/build/arch/"+arch+"/include");
- cflags->push_back("-I" + kdir_ + "/build/arch/"+arch+"/include/generated/uapi");
+ cflags->push_back("-Iarch/"+arch+"/include/");
  cflags->push_back("-I" + kdir_ + "/build/arch/"+arch+"/include/generated");
+ cflags->push_back("-Iinclude");
  cflags->push_back("-I" + kdir_ + "/build/include");
- cflags->push_back("-I" + kdir_ + "/build/./arch/"+arch+"/include/uapi");
+ cflags->push_back("-Iarch/"+arch+"/include/uapi");
  cflags->push_back("-I" + kdir_ + "/build/arch/"+arch+"/include/generated/uapi");
- cflags->push_back("-I" + kdir_ + "/build/include/uapi");
- cflags->push_back("-I" + kdir_ + "/build/include/generated");
+ cflags->push_back("-Iinclude/uapi");
  cflags->push_back("-I" + kdir_ + "/build/include/generated/uapi");
+ } else {
+ cflags->push_back("-Iarch/"+arch+"/include/");
+ cflags->push_back("-Iarch/"+arch+"/include/generated");
+ cflags->push_back("-Iinclude");
+ cflags->push_back("-Iarch/"+arch+"/include/uapi");
+ cflags->push_back("-Iarch/"+arch+"/include/generated/uapi");
+ cflags->push_back("-Iinclude/uapi");
+ cflags->push_back("-Iinclude/generated/uapi");
  }
 
- cflags->push_back("-I./arch/"+arch+"/include");
- cflags->push_back("-Iarch/"+arch+"/include/generated/uapi");
- cflags->push_back("-Iarch/"+arch+"/include/generated");
- cflags->push_back("-Iinclude");
- cflags->push_back("-I./arch/"+arch+"/include/uapi");
- cflags->push_back("-Iarch/"+arch+"/include/generated/uapi");
- cflags->push_back("-I./include/uapi");
- cflags->push_back("-Iinclude/generated/uapi");
  cflags->push_back("-include");
  cflags->push_back("./include/linux/kconfig.h");
  cflags->push_back("-D__KERNEL__");